Most of the evolved 3rd generation wireless communication systems, including 3rd Generation Partnership Project (3GPP) Long Term Evolution (LTE), 3GPP LTE-Advanced (LTE-A), and Institute of Electrical and Electronics Engineers (IEEE) 802.16m, have adopted Orthogonal Frequency Division Multiplexing (Multiple Access) (OFDM(A)) as a multi-carrier multiple access scheme.
In the downlink of a wireless communication system adopting multi-carrier multiple access, a base station (e.g., evolved Node B (eNB)) allocates resources to a terminal (e.g., User Equipment (UE) and Mobile station (MS)) for data transmission in units of a Resource Block (RB) which is composed of a plurality of subcarriers and a plurality of OFDM symbols.
In transmission, the base station can use spatial multiplexing and transmission diversity. In a 3GPP LTE or LTE-A system, transmission diversity includes applying precoding to codewords mapped to individual layers and mapping the precoded codewords to the Resource Elements (REs) of the RBs allocated to the corresponding terminals. In the 3GPP LTE-A system, a Demodulation Reference Signal (DM-RS), for demodulating, at the UEs, the received signal, and a Channel State Information Reference Signal (CSI-RS), for measuring the channel state, are introduced. However, these reference signals are not being used in the 3GPP LTE system. With the introduction of the DM-RS and CSI-RS, the resource locations for data transmission are changed as compared to the conventional LTE system and, as a consequence, the precoding and resource mapping designed for use in the LTE system for transmission diversity cannot be applied to the LTE-A system without performance degradation.